1. Field of the Invention
The present invention relates to a hydraulic control device which is suitable for an automatic transmission mechanism mounted on a vehicle, in particular to a hydraulic control device suitable for an automatic transmission having forward four speed modes, in detail, a hydraulic control device which is able to make a certain speed shift by a manual shift lever when electric failures occur.
1. Description of the Prior Art
A fail-safe mechanism which is able to conduct shifting operation to a certain degree by a manual shift lever is incorporated in the automatic transmission, in order not to disable controlling of the automatic transmission too soon even at electric accidents.
Conventionally, a four speed automatic transmission composed of a main automatic transmission mechanism and a sub transmission mechanism to change an under-drive (or an over-drive) and direct driving employs a hydraulic control device composed of two solenoid valves for shifting and three shift valves. The four speed automatic transmission, when the two solenoid valves are under non-electrified condition due to electric failure and the like, is designed to be changed to a first speed at an L range of a manual shift lever, to be changed to third speed at a 2 range and to be over-drive (fourth speed) at a D range.
The applicant of the present invention has proposed an hydraulic device for a forward four or five speed automatic transmission including a manual shift lever (manual valve) having seven positions (1, 2, 3, D, N, R, P ranges), as shown in the Japanese Laid Open Patent Application No. Sho-63-1394. This hydraulic control device, when all the solenoid valves are under non-electrified condition, is designed to be changed to a second speed at a 1 range, to be changed to a second speed at a 2 range, to be changed to a third speed at a 3 range and to be changed to a fourth speed at a D range.
In the hydraulic control device in the automatic transmission composed of the seven positions, a second speed mode is set at a 1 range, which forces a vehicle to start from a second speed mode by the manual shift lever when electric failures occur, although it is, in respect of safety and efficiency of a vehicle, desirable to let each shifting speed correspond to each ranges, when all the solenoid valve are under non-electrified condition due to electric failures. For example, by control of a manual shift lever a P range corresponds to parking, an R range to reverse running, an N range to neutral, a D range to fourth speed mode (over-drive), a 3 range to third speed mode, a 2 range to second speed mode and a 1 range to first speed mode.
If other solenoid valves are used so that each shifting speed corresponds to each range, the reliability of fail-safe mechanism at an electric failure declines and a cost-up of a automatic transmission is caused.